EP0040166B1 - Industrial chimney with forced draught - Google Patents

Description

The present invention refers to industrial chimneys intended for discharging gaseous products into the atmosphere which we want to get rid of, this term gaseous products including vapors and solid or liquid particles suspended in a gas. The most frequent case is that of combustion products from fireplaces, ovens and the like.

To minimize the annoyance and pollution that these products can cause, the corresponding chimneys should be as high as possible, which leads to expensive constructions.

In order to avoid this drawback, it has been proposed in FR-A-1 350 587 to reject under pressure the gases to be evacuated through a converging nozzle disposed at the top of the chimney, this nozzle being surrounded by a wall cut out with openings. The jet leaving the nozzle sucks through these openings a current of air which constitutes around it a sort of protective insulating sheath intended to delay the condensation of the humidity of the gases and the formation of a corresponding plume of smoke. Small vertical vents drilled in the base of the nozzle facilitate air entrainment. By the very fact of this drive, the air sheath rises at a lower speed than that of the central jet of gaseous product to be evacuated, so that in the contact zone between this jet and the sheath, vortices are formed which produce a rapid mixing between air and gas, so that the elevation of the smoke plume remains very limited.

FR-A- 2122026 discloses a solution according to which the chimney comprises a central column for the flow of the gases to be evacuated, surrounded by a cylindrical sleeve in which air is blown under pressure. The column and the sleeve opening vertically substantially in the same horizontal plane, the air comes out in the form of a duct which again delays the condensation of humidity and the formation of a plume of smoke. But the upward speed provided for the air duct is in principle higher than that of the gaseous products to be discharged, so that here again there is a phenomenon of rapid mixing which considerably reduces the advantages of the device. In addition, even if it were desired that these two gas velocities be equal, it would be very difficult to obtain it constantly despite the variations in the regimes of the hearth producing the gases to be evacuated.

It is also known to blow air into a chimney to dilute the combustion gases. In DE-A-2 730 582 a corresponding device is described according to which the air blowing pipe is arranged in the axis of a Venturi produced in the upper part of the chimney. But it is understood that with such a device the air jet is at the center of the gas stream to be evacuated and can in no way constitute a protective sheath isolating it from the surrounding atmosphere.

The same remark applies to devices, such as that described in FR-A 1 056 616, in which, in order to improve the operation of the combustion apparatuses and to ensure the evacuation of the fumes, one injects into an axial tube. provided on the smoke path, of the air taken from the premises where the fumes are likely to appear.

The invention aims to solve the problem of the elevation of the plume of smoke resulting from the condensation of the humidity of the combustion gases in a more efficient manner than has hitherto been possible. According to this invention, a chimney for the evacuation into the atmosphere of combustion gases or the like, comprising a central column for the flow of the stream of gaseous products to be evacuated and an outer wall which surrounds this column at least in its upper part by providing an annular space in which air passes intended to form around at least a fraction of the periphery of this gas stream, a protective sheath delaying the formation of the smoke plume, and of the kind also in which the central column is surmounted by a converging nozzle whose inlet diameter is substantially equal to that of the upper end of said column, is characterized in that it comprises immediately below the base of the nozzle (1 a) radial discharge openings (4) which extend substantially over its entire periphery to communicate the annular space (3) with the interior of the central column (1), while it st provided means for sending into said annular space (3) air or other auxiliary gas so that it passes through said openings (4) in a substantially centripetal direction while being in overpressure relative to said stream of gaseous products to evacuate, at these openings.

• Fig. 1 est une coupe d'une cheminée suivant l'invention avec indication schématique de l'installation correspondante.
• Fig. 2 montre schématiquement comment se comporte cette cheminée en fonctionnement.

The appended drawing, given by way of example, will allow a better understanding of the invention, the characteristics which it presents and the advantages which it is likely to provide:

• Fig. 1 is a section through a chimney according to the invention with schematic indication of the corresponding installation.
• Fig. 2 schematically shows how this chimney behaves in operation.

The chimney shown in fig. 1 comprises a central column 1 established in any suitable manner, for example in bricks, and an outer wall 2 made for example of concrete, reinforced or unreinforced, and which surrounds the column 1 by providing an intermediate annular space 3. The column 1 is ends at the top with a part 1 a of smaller diameter suitable for forming a nozzle or nozzle. In the embodiment shown, this part 1a is cylindrical, but it is perfectly possible to provide it converging over at least part of its height. As for the outer wall 2, it is connected to the column 1 towards the base of the part or nozzle 1 a, as indicated in 2a.

The connection between the column 1 and the nozzle 1 a is effected by a rounded part 1 b immediately below which there are provided openings 4 which make the annular space 3 communicate with the interior of the column.

The hearth, oven or other device 5 which generates the gaseous products to be evacuated is connected to the base of the column 1 by a pipe 6 (shown diagrammatically by a single line) on which a blower fan 7 is inserted, so as to achieve what 'it was agreed to call the forced draw. Of course, the line 6 could also include any filtration, purification, cooling, dehumidification or other treatment devices that one could desire. For its part, the intermediate annular space 3 receives via a pipe 8 the air discharged by a fan 9. There is also provided a pressure comparator 10 connected to the respective pipes 6 and 8 by branches 11 and 12, this comparator acting on the fan 9 via any suitable connection, for example mechanical or electrical, which has been shown diagrammatically by the broken line 13.

During operation, the fan 7 discharges the gaseous products to be discharged into the base of the column 1 under a certain overpressure. At the same time the fan 9 discharges air into the intermediate space 3 under a pressure which the pressure gauge 10 maintains very slightly greater than that generated by the fan 7. Under these conditions at the base of the nozzle 1 a l air from space 3 exits radially through the openings 4 in a centripetal direction and mixes with the mass of gaseous proudits which rises in column 1, the assembly being evacuated at high speed by the nozzle 1 a in which the static pressure is transformed into dynamic pressure, that is to say into kinetic energy.

• 1 °) Du fait qu'une fraction de l'air se mélange aux gaz à évacuer, le jet qui sort de la tuyère 1 a reste sans solution de continuité dans le sens transversal. En d' autres termes il n'y a pas de séparation entre une lame d'air extérieure et une masse centrale de produits gazeux.
• 2°) La gaine d'air presque pur qui adhère au jet central de produits gazeux est relativement sèche et isolante au point de vue thermique. Elle retarde donc considérablement les phénomènes de condensation qui n'apparaissent qu'à une hauteur notable au-dessus de la tuyère 1 a.
• 3°) Du fait de la communication assurée entre l'espace 3 et la colonne 1 par les ouvertures 4 il se produit à l'entree de la tuyère 1 a un phénomène d'auto-régulation des pressions respectives de l'air et des produits gazeux à évacuer. En effet le débit de l'air à travers les ouvertures 4 est fonction non pas de la pression de refoulement du ventilateur 9, mais bien de la différence entre cette pression et celle de tirage forcé assurée par le ventilateur 7. Par conséquent les pertes de charges entre la sortie du ventilateur d'air 9 et le débouché desdites ouvertures 4 sont également fonction de cette différence. Il en résulte que les petites erreurs de réglage du mano-compensateur 10 lors des variations d'allure du four 5 sont automatiquement compensées par ces pertes de charge. Si par exemple lors d'une réduction de cette allure et donc de la pression de tirage dans la colonne 1 le mano-comparateur 10 impose au ventilateur 9 une pression de refoulement trop forte, les pertes de charge interviennent efficacement pour limiter une trop importante augmentation du débit d'air.

It is however very important to note that in reality the air which leaves the openings 4 preferentially flows against the wall of the nozzle 1 a, so that at the exit of this one is in the presence of a gas jet whose periphery is almost exclusively constituted by air. This conformation has many advantages:

• 1) Due to the fact that a fraction of the air mixes with the gases to be evacuated, the jet which leaves the nozzle 1 a remains without a solution of continuity in the transverse direction. In other words, there is no separation between an external air space and a central mass of gaseous products.
• 2) The almost pure air duct which adheres to the central jet of gaseous products is relatively dry and thermally insulating. It therefore considerably delays the condensation phenomena which appear only at a significant height above the nozzle 1 a.
• 3 °) Due to the communication ensured between the space 3 and the column 1 by the openings 4 it occurs at the inlet of the nozzle 1 has a phenomenon of self-regulation of the respective pressures of the air and gaseous products to be removed. Indeed, the air flow through the openings 4 is not a function of the discharge pressure of the fan 9, but rather of the difference between this pressure and that of forced draft provided by the fan 7. Consequently the losses of charges between the outlet of the air fan 9 and the outlet of said openings 4 are also a function of this difference. As a result, the small adjustment errors of the pressure compensator 10 during variations in the shape of the oven 5 are automatically compensated by these pressure drops. If for example during a reduction of this speed and therefore of the drawing pressure in column 1 the pressure comparator 10 imposes on the fan 9 a too high discharge pressure, the pressure drops intervene effectively to limit an excessive increase air flow.

It can also be noted that the presence of air in very slight overpressure in space 3 avoids all the seepage through the joints of the column 1 (especially when the latter is made of bricks). In addition, the wall of this column is subjected on its two faces to almost equal pressures and runs no risk of bursting. As for the outer wall 2, even if it has slight leaks, this is immaterial since it is then air which escapes towards the exterior.

We have schematically shown in FIG. 2 the general appearance of the gas jet 14 leaving a chimney according to the invention. This imports a height H. The jet 14 of combustion gases or the like and the peripheral air rises first vertically, then gradually tilts under the effect of the wind (indicated by arrow 15). The horizontal plume 16 only appears at a height h above the nozzle 1 a, so that from this point of view everything happens as if we were dealing with a conventional chimney of height H + h . It should also be noted that due to the delay in condensation, the jet 14 is at first perfectly transparent and practically invisible. It only takes the usual white color very gradually, for example at the level indicated in 14a. We could also increase this action of the auxiliary air by pre-treating it by heating and / or dehydration before discharging it into space 3.

. It should also be noted in this regard that the auxiliary air is automatically heated by heat exchange with the wall of the column 1. This has the double advantage of reducing the energy required to obtain a determined temperature of this air at the outlet of the openings 4, on the other hand, to avoid excessive heating of said wall in the case of very hot gaseous products.

It should moreover be understood that the above description has been given only by way of example and that it in no way limits the field of the invention from which one would not depart by replacing the execution details described by all other equivalents. The auxiliary gas could be other than atmospheric air. We could treat it before sending it to space 3. Although it is particularly advantageous to make this space 3 over the entire height of the chimney to the nozzle 1 a, we could, if necessary, reduce it to a sort of groove surrounding the openings 4 and which a pipe parallel to the column 1 would connect to the fan 9.

Claims (4)

1.) Chimney for the evacuation of combustion gas or other into the atmospere, of the type comprising a central column (1) for the flow of the current of gaseous products which are to be evacuated and an exterior wall (2) which surrounds this column at least in its upper part providing an annular space (3) in which air passes intended to form, around a fraction at least of the periphery of this gaseous current, a protective guard retarding the formation of a wreath of smoke, and of the type also in which the central column (1) is surmounted by a convergent pipe (1 a) the entry diameter of which is substantially equal to that of the upper extremity of the said column, characterized in that it comprises immediately beneath the base of the pipe (1 a) radial discharge openings (4)which extend substantially over all its periphery to connect the annular space (3) with the interior of the central column (1), whilst means are provided to carry air or other auxiliary gas into the said annular space (3) so that it traverses said openings (4) in a substantially centripetal direction and is in over-pressure in relation to the said current of gaseous products which are to be evacuated, at the level of these openings.

2.) Chimney according to claim 1, characterized in that the exterior wall (2) becomes flush with the central column (1) immediately above the injection openings (4) and beneath the pipe.

3.) Chimney according to any one of the preceding claims, characterized in that it comprises means (mano-comparator 10) to automatically regulate at its base the delivery pressure of the auxiliary gas at a value slightly greater than that of the blowing of the gaseous products which are to be evacuated.

4.) Chimney according to any one of the preceding claims, characterized in that the auxiliary gas is treated before being discharged into the gaseous products which are to be evacuated, so as to lower its relative and/or absolute humidity and to reduce and/or retard the formation of the wreath of vapour above the outlet of the said chimney.

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